1. Field of the Invention
The present invention relates to a substrate for a display panel, a display panel having the substrate, a method of producing the substrate, and a method of producing the display panel. The present invention specifically relates to a substrate for a display panel produced by a production method including a step of forming a photoresist pattern of a given shape by divisional exposure, a display panel having the substrate, a method of producing the substrate, and a method of producing the display panel.
2. Description of the Related Art
A generally used liquid crystal display panel has two substrates which are placed opposed to each other having a minute gap therebetween, and liquid crystals are sealed in between the substrates. On one of the substrates, pixel electrodes are arranged in a matrix, and elements such as thin film transistors arranged to apply voltages to the pixel electrodes, data signal lines (source signal lines) and scanning signal lines (gate signal lines) are provided. On the other substrate, elements such as a black matrix and color layers of red, green and blue colors are arranged in a matrix, and elements such as transparent electrodes (common electrodes) are provided on those elements.
Some of the above-mentioned elements are formed by photolithography. For example, the thin film transistors, the black matrix, and the color layers are preferably formed by steps of coating a photoresist material on the substrate, performing exposure on the coated photoresist material via a photomask, and removing unnecessary portions of the photoresist material.
In the step of performing exposure on the coated photoresist material via the photomask, the divisional exposure is preferably used. The divisional exposure is performed by arbitrarily designating a specific pattern or range in a pattern formed on the photomask, dividing a region to be exposed into some regions, and performing exposure on the divided regions while performing screen composition of a product pattern on the substrate. Owing to such divisional exposure, it is possible to perform exposure on a large area region to be exposed with a small area photomask. Thus, the cost of the photomask can be decreased.
However, in such divisional exposure, if the display panel does not fall within one photomask, there is no other choice but to set the boundary between the divided regions (hereinafter, referred to as “divided exposure regions”) within a display region of the display panel. In addition, if there is a deviation between the divided exposure regions for some reasons, the patterns, which should be ordinarily formed continuously over the entire display region of the display panel, become discontinuous at the boundary between the divided exposure regions.
When the exposure deviation becomes great, the following problems could arise. If the patterns of the elements formed within the display region are discontinuous at the boundary between the divided exposure regions, positional relations between the elements provided on one of the substrates and the elements provided on the other substrate differ with each divided exposure region when the two substrates are opposed and bonded to each other. Therefore, display properties of liquid crystals could differ with each divided exposure region. In addition, properties of the elements provided on the substrate could differ with each divided exposure region. In addition, these differences could be visually observed as streaky luminance differences or color irregularities at the boundary between the divided exposure regions.
Therefore, in order to produce a liquid crystal display panel excellent in display quality, it is necessary to make inspection for the luminance differences or color irregularities caused by the exposure deviation after production of the liquid crystal display panel. If the exposure deviation is detected by the inspection, it is necessary to grasp occurrence trend and make process management and evaluation.
As a prior art literature relating to the present invention, Japanese Patent Application Unexamined Publication No. 2000-231184 is cited.
There are a plurality of elements to be formed by the divisional exposure. Therefore, in order to make process management and evaluation, it is necessary to specify of which element the boundary between the divided exposure regions where the luminance differences or color irregularities detected by the inspection occur is.
However, if the boundary between the divided exposure regions of one element coincides with the boundary between the divided exposure regions of the other element, it becomes difficult to specify of which element the boundary between the divided exposure regions where the streaky luminance differences or color irregularities detected by the inspection occur is. Thus, process management and evaluation become also difficult.
In addition, even if the boundary between the divided exposure regions of one element does not coincide with the boundary of the divided exposure regions of the other element, it is first necessary to grasp where the boundary between the divided exposure regions of each element is positioned on the substrate. In other words, if streaky luminance differences or color irregularities are detected by the inspection in a producing step, it is necessary to check the occurrence position of the streaky luminance differences or color irregularities by making measurement on the display panel by means of a measure, and check against a design drawing to specify of which element the boundary between the divided exposure regions where the luminance differences or color irregularities detected by the inspection occur is. Thus, much effort is required in making the inspection.
In addition, it is necessary to check whether streaky luminance differences or color irregularities are occurring at the boundary between the divided exposure regions of each element at the time of checking quality of produced display panels. In such a situation, it is necessary to make measurement on the display panel by means of a measure in order to grasp where the boundary between the divided exposure regions of each element is positioned. Thus, much effort is required in checking quality of the display panel.